Methods and systems for performing antenna pointing while mitigating interference with a nearby satellite

ABSTRACT

Systems and methods are described herein for performing mispointing correction operations that can provide accurate pointing of an antenna towards a satellite, while also satisfying interference requirements with other satellites. As a result, the mispointing correction operations described herein can improve resource efficiency of communication systems using such antennas and help ensure compliance with interference requirements of other satellites.

CROSS REFERENCE

The present Application for Patent is a Continuation of U.S. patentapplication Ser. No. 15/269,355 by Petranovich et al., entitled “METHODSAND SYSTEMS FOR PERFORMING ANTENNA POINTING WHILE MITIGATINGINTERFERENCE WITH A NEARBY SATELLITE,” filed Sep. 19, 2016, assigned tothe assignee hereof, and expressly incorporated herein.

BACKGROUND

The present disclosure relates generally to satellite communications,and more specifically to systems and methods for accurate antennapointing in satellite communications while avoiding excessiveinterference with one or more non-target satellites.

An Earth-based antenna terminal for communication with a satellitetypically has high antenna gain and a narrow beam pointed at thesatellite, because of the large distance to the satellite and to avoidinterference with other satellites. Mobile antenna terminals can includea positioner to maintain pointing (or tracking) of the beam of theantenna at the satellite during movement.

Pointing error (or misalignment) between the boresight direction ofmaximum gain of the beam and the actual direction of the satellite canhave a detrimental effect on the quality of the link between the antennaand the satellite. Small misalignment may be compensated for by reducinga modulation and coding rate of signals communicated between the antennaand the satellite. However, to maintain a given data rate (e.g.,bits-per-second (bps)), this approach may increase system resource usageand thus result in inefficient use of the resources. Pointing error canalso make it more challenging to ensure compliance with interferencerequirements with other satellites that are imposed by regulatoryagencies (e.g., FCC, ITU, etc.) and/or a coordination agreement withoperators of the other satellites.

The pointing error may increase with time due to various factors such asdrift of a sensor (e.g., an inertial reference unit (IRU)) associatedwith mobile antenna terminal, structural deflections caused by movementand other disturbances, etc. In order to correct this pointing error,the mobile antenna terminal may occasionally perform a signal-basedmispointing correction operation such as steptrack, conical scan andsimilar methods. The mispointing correction operation can include movingthe beam of the antenna in an attempt to determine the direction atwhich a signal metric (e.g., signal strength) of a signal communicatedwith satellite is maximized.

SUMMARY

In one embodiment, a method is described that includes communicating asignal between an antenna system on a mobile vehicle and a targetsatellite. The method further includes obtaining a current geographiclocation of the mobile vehicle. The method further includes determiningif the current geographic location is within an acceptable geographicregion for performing a first mispointing correction operation of theantenna system. The acceptable geographic region corresponds tointerference by the communicated signal with a non-target satellite dueto the first mispointing correction operation that is below a threshold.The method further includes performing the first mispointing correctionoperation of the antenna system if the current geographic location iswithin the acceptable geographic region.

In another embodiment, an antenna system for mounting on a mobilevehicle is described. The antenna system includes an antenna having abeam for communicating a signal with a target satellite. The antennasystem further includes a pointing adjustment mechanism coupled to theantenna and responsive to a control signal to adjust an angular positionof the beam of the antenna. The antenna system further includes anantenna control unit to obtain a current geographic location of themobile vehicle. The antenna control unit further determines if thecurrent geographic location is within an acceptable geographic regionfor performing a first mispointing correction operation of the antennasystem. The acceptable geographic region corresponds to interference bythe communicated signal with a non-target satellite due to the firstmispointing correction operation that is below a threshold. The antennacontrol unit further provides the control signal to the pointingadjustment mechanism to perform the first mispointing correctionoperation of the antenna system if the current geographic location iswithin the acceptable geographic region.

Other aspects and advantages of the present disclosure can be seen onreview of the drawings, the detailed description, and the claims whichfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example satellite communications system in whichan antenna system as described herein can be used to provide veryaccurate pointing towards a satellite while also avoiding excessiveinterference with one or more other satellites.

FIG. 2 is a block diagram illustrating an example antenna system on theaircraft of FIG. 1.

FIG. 3 illustrates a perspective view of an example of an antenna andpositioner of an example antenna system described herein.

FIG. 4 illustrates an example process for operating the antenna systemincluding performing an example re-pointing process by the antennacontrol unit of FIG. 2.

FIG. 5 illustrates an example of a correction profile of the firstmispointing correction operation versus azimuth and elevation angles.

FIG. 6 illustrates an example of an acceptable geographic region forperforming the first mispointing correction operation.

FIG. 7 illustrates an example process for operating the antenna systemincluding performing an example re-pointing process by the antennacontrol unit of FIG. 2.

FIG. 8 illustrates example of a correction profile of a secondmispointing correction operation as described herein.

FIG. 9 illustrates an example process for operating the antenna systemincluding performing the example re-pointing process of FIG. 7.

FIG. 10 illustrates another example process for operating the antennasystem including performing the example re-pointing process of FIG. 7.

FIG. 11 illustrates another example process for operating the antennasystem including performing example re-pointing process of FIG. 7.

FIG. 12 illustrates another example process for operating the antennasystem 150 including performing the example re-pointing process of FIG.7.

DETAILED DESCRIPTION

Systems and methods are described herein for performing mispointingcorrection operations of a mobile antenna system that can be used toprovide accurate pointing of an antenna towards a satellite (e.g., ageostationary satellite), while also satisfying interferencerequirements with one or more other satellites. In particular, themispointing correction operations described herein take intoconsideration the interference requirements of the other satellites. Indoing so, the mobile antenna system can correct pointing errors fromtime to time in order to maintain accurate pointing at the satellite,while also avoiding excessive interference that could result due tointentional mispointing introduced during the mispointing correctionoperations.

As a result, the mispointing correction operations described herein canimprove resource efficiency of communication systems using suchantennas. For example, achieving accurate pointing may reduce thenecessary system resources for maintaining a given data rate byincreasing the allowable coding rate (e.g., decreasing data redundancy),which may increase overall system performance.

FIG. 1 illustrates an example satellite communications system 100 inwhich an antenna system 150 as described herein can be used to providevery accurate pointing towards satellite 110 (referred to hereinafter as“target satellite 110”) while also avoiding excessive interference withone or more other satellites. Many other configurations are possiblehaving more or fewer components than the satellite communications system100 of FIG. 1.

In the illustrated embodiment, the antenna system 150 is mounted onaircraft 102, which in this example is an airplane. More generally, theantenna system 150 can be mounted on various types of mobile vehiclessuch as aircraft (e.g., airplanes, helicopters, drones, blimps,balloons, etc.), trains, automobiles (e.g., cars, trucks, busses, etc.),watercraft (e.g., private boats, commercial shipping vessels, cruiseships, etc.) and others. In the following examples, the techniquesdescribed herein for performing mispointing correction operations aredescribed in conjunction the aircraft 102. Alternatively, themispointing correction operations may be used in conjunction with othermobile vehicles such as those mentioned above.

As described in more detail below, the antenna system 150 includes anantenna 152 producing a beam that facilitates communication between theaircraft 102 and the target satellite 110. In the illustratedembodiment, the antenna 152 is an array of waveguide antenna elementsarranged in a rectangular panel. Each of the one or more antennaelements can include a waveguide-type feed structure including a hornantenna. Alternatively, the antenna 152 may be a different type ofantenna, such as a reflector antenna, a phased array, a slot array, etc.

The antenna system 150 also includes a pointing adjustment mechanismsuch as a mechanical positioner (not shown) responsive to a controlsignal from an antenna control unit (not shown) to provide very accuratepointing of the beam of the antenna 152 at the target satellite 110using the techniques described herein. In some embodiments describedherein the antenna system 150 is used for bidirectional (two-way)communication with the target satellite 110. In other embodiments, theantenna system 150 may be used for unidirectional communication with thetarget satellite 110, such as a receive-only implementation (e.g.,receiving satellite broadcast television). Although only one antennasystem 150 is illustrated in FIG. 1 to avoid over complication of thedrawing, the satellite communications system 100 may include manyantenna systems 150.

As used herein, a beam of an antenna that is pointed at a targetsatellite has sufficient antenna gain in the direction of the satelliteto permit communication of one or more signals. The communication can bebidirectional (i.e., the antenna transmits a signal to the satellite andalso receives a signal from the satellite) or unidirectional (i.e., theantenna either transmits a signal to the satellite or receives a signalfrom the satellite, but not both). The direction of the target satellitemay be the boresight direction of maximum gain of the beam.Alternatively, the gain of the beam in the direction of the targetsatellite may be less than the maximum gain of the beam. This may forexample be due to pointing accuracy limitations of the antenna. Thedifference between the boresight direction of the beam and the directionof the target satellite is referred to herein as the pointing error.

In the illustrated embodiment, the target satellite 110 providesbidirectional communication between the aircraft 102 and a gatewayterminal 130. The gateway terminal 130 is sometimes referred to as a hubor ground station. The gateway terminal 130 includes an antenna totransmit a forward uplink signal 140 to the target satellite 110 andreceive a return downlink signal 142 from the target satellite 110. Thegateway terminal 130 can also schedule traffic to the antenna system150. Alternatively, the scheduling can be performed in other parts ofthe satellite communications system 100 (e.g., a core node, or othercomponents, not shown). Signals 140, 142 communicated between thegateway terminal 130 and the target satellite 110 can use the same,overlapping, or different frequencies as signals 114, 116 communicatedbetween the target satellite 110 and the antenna system 150.

Network 135 is interfaced with the gateway terminal 130. The network 135can be any type of network and can include for example, the Internet, anIP network, an intranet, a wide area network (WAN), a virtual LAN(VLAN), a fiber optic network, a cable network, a public switchedtelephone network (PSTN), a public switched data network (PSDN), apublic land mobile network, and/or any other type of network supportingcommunication between devices as described herein. The network 135 caninclude both wired and wireless connections as well as optical links.The network 135 can connect multiple gateway terminals 130 that can bein communication with target satellite 110 and/or with other satellites.

The gateway terminal 130 can be provided as an interface between thenetwork 135 and the target satellite 110. The gateway terminal 130 canbe configured to receive data and information directed to the antennasystem 150 from a source accessible via the network 135. The gatewayterminal 130 can format the data and information and transmit forwarduplink signal 140 to the target satellite 110 for delivery to theantenna system 150. Similarly, the gateway terminal 130 can beconfigured to receive return downlink signal 142 from the targetsatellite 110 (e.g., containing data and information originating fromthe antenna system 150) that is directed to a destination accessible viathe network 135. The gateway terminal 130 can also format the receivedreturn downlink signal 142 for transmission on the network 135.

The target satellite 110 can receive the forward uplink signal 140 fromthe gateway terminal 130 and transmit corresponding forward downlinksignal 114 to the antenna system 150. Similarly, the target satellite110 can receive return uplink signal 116 from the antenna system 150 andtransmit corresponding return downlink signal 142 to the gatewayterminal 130. The target satellite 110 can operate in a multiple spotbeam mode, transmitting and receiving a number of narrow beams directedto different regions on Earth. Alternatively, the target satellite 110can operate in wide area coverage beam mode, transmitting one or morewide area coverage beams.

The target satellite 110 can be configured as a “bent pipe” satellitethat performs frequency and polarization conversion of the receivedsignals before retransmission of the signals to their destination. Asanother example, the target satellite 110 can be configured as aregenerative satellite that demodulates and remodulates the receivedsignals before retransmission.

As shown in FIG. 1, the satellite communications system 100 alsoincludes another satellite 120 (hereinafter referred to as “non-targetsatellite 120”). Communication of one or more signals between thenon-target satellite 120 and the antenna system 150 is undesired orunintended. Although only one non-target satellite 120 is illustrated inFIG. 1 to avoid over complication of the drawing, the satellitecommunications system 100 can include many more non-target satellites120 and the techniques described herein can be used to avoid excessiveinterference with each of the non-target satellites 120.

The non-target satellite 120 can, for example, be configured as a bentpipe or regenerative satellite. The non-target satellite 120 cancommunicate one or more signals with one or more ground stations (notshown) and/or other terminals (not shown).

As mentioned above, the antenna system 150 includes antenna 152 thatproduces a beam pointed at the target satellite 110 via the pointingadjustment mechanism to provide for transmission of the return uplinksignal 116 and reception of the forward downlink signal 114. Based onthe location of the target satellite 110 and the location and attitude(yaw, roll and pitch) of the aircraft 102, the antenna control unit ofthe antenna system 150 provides a control signal to the pointingadjustment mechanism to change the angular position of the beam tomaintain pointing of the beam of the antenna 152 at the target satellite110 as the aircraft 102 moves. However, various factors such as drift ofa navigation sensor (e.g., an inertial reference unit (IRU)) on theaircraft 102, structural deflections of the aircraft 102 caused bytakeoff, movement and other disturbances, etc., can cause the pointingerror to increase with time.

Thus, from time-to-time, the antenna control unit also providesappropriate values of the control signal to the pointing adjustmentmechanism to perform a mispointing correction operation, while alsoavoiding excessive interference with the non-target satellite 120, usingthe techniques described herein. In particular, the mispointingcorrection operation takes into consideration the interferencerequirement of the non-target satellite 120, so that excessiveinterference with the non-target satellite 120 is avoided. Themispointing correction operation is described in more detail below withrespect to subsequent Figures.

As used herein, interference “with” the non-target satellite 120 canrefer to uplink interference and/or downlink interference. Uplinkinterference is interference to the non-target satellite 120 caused by aportion of the return uplink signal 116 transmitted by the antennasystem 150 that is received by the non-target satellite 120. Downlinkinterference is interference to the antenna system 150 caused by aportion of a signal transmitted by the non-target satellite 120 that isreceived by the antenna system 150.

In the illustrated embodiment, the target satellite 110 and thenon-target satellite 120 are each geostationary satellites. Thegeostationary orbit slots, and thus the angular separation along thegeostationary arc between the target satellite 110 and the non-targetsatellite 120, can vary from embodiment to embodiment. In someembodiments, the angular separation along the geostationary arc is atleast two degrees. In alternative embodiments, one or both of the targetsatellite 110 and the non-target satellite 120 can be anon-geostationary satellite, such as a LEO or MEO satellite.

FIG. 2 is a block diagram illustrating an example antenna system 150 onthe aircraft 102 of FIG. 1. Many other configurations are possiblehaving more or fewer components than the antenna system 150 shown inFIG. 2. Moreover, the functionalities described herein can bedistributed among the components in a different manner than describedherein.

The antenna system 150 includes antenna 152 that is housed under radome200 disposed on the top of the fuselage or other location (e.g., on thetail, etc.) of the aircraft 102. The antenna 152 produces a beam thatcan provide for transmission of the return uplink signal 116 andreception of the forward downlink signal 114 to support two-way datacommunication between data devices 260 within the aircraft 102 and thenetwork 135 via target satellite 110 and gateway terminal 130. The datadevices 260 can include mobile devices (e.g., smartphones, laptops,tablets, netbooks, and the like) such as personal electronic devices(PEDs) brought onto the aircraft 102 by passengers. As further examples,the data devices 260 can include passenger seat back systems or otherdevices on the aircraft 102. The data devices 260 can communicate withnetwork access unit 340 via a communication link that can be wired orwireless. The communication link can be, for example, part of a localarea network such as a wireless local area network (WLAN) supported bywireless access point (WAP) 250. One or more WAPs can be distributedabout the aircraft 102, and can, in conjunction with network access unit240, provide traffic switching or routing functionality. The networkaccess unit 240 can also allow passengers to access one or more servers(not shown) local to the aircraft 102, such as a server that providesin-flight entertainment.

In operation, the network access unit 240 can provide uplink datareceived from the data devices 260 to modem 230 to generate modulateduplink data (e.g., a transmit IF signal) for delivery to transceiver210. The transceiver 210 can then upconvert and then amplify themodulated uplink data to generate the return uplink signal 116 fortransmission to the target satellite 110 via the antenna 152. Similarly,the transceiver 210 can receive the forward downlink signal 114 from thetarget satellite 110 via the antenna 152. The transceiver 210 canamplify and then downconvert the forward downlink signal 114 to generatemodulated downlink data (e.g., a receive IF signal) for demodulation bythe modem 230. The demodulated downlink data from the modem 230 can thenbe provided to the network access unit 240 for routing to the datadevices 260. The modem 230 can be integrated with the network accessunit 240, or can be a separate component, in some examples.

In the illustrated embodiment, the transceiver 210 is located outsidethe fuselage of the aircraft 102 and under the radome 200.Alternatively, the transceiver 210 can be located in a differentlocation, such as within the aircraft interior.

In the illustrated embodiment and subsequent examples, the antennasystem 150 includes positioner 220 coupled to the antenna 152.Alternatively, the antenna system 150 may include a different pointingadjustment mechanism that may vary from embodiment to embodiment, andmay depend on the antenna type of the antenna 152.

The positioner 220 is responsive to a control signal on line 272 fromantenna control unit 270 to mechanically point the beam of the antenna152 in the direction of the target satellite 110 as the aircraft 102moves. Accordingly, the values of the control signal on line 272 toadjust the angular position of the beam depend on the manner in whichthe positioner 220 (or other pointing adjustment mechanism) iscontrolled, and can vary from embodiment to embodiment. Although only asingle line 272 and a single control signal are shown in FIG. 2, as usedherein “control signal” can include one or more separate control signalsprovided by the antenna control unit 270 to the positioner 220 (or otherpointing adjustment mechanism), which in turn may be provided on one ormore lines. For example, in some embodiments in which the pointingadjustment mechanism adjusts the angular position of the beam inmultiple axes (e.g., azimuth and elevation), the control signal includesa control signal indicating the angular value of each axis.

In some embodiments, the boresight direction of the beam of the antenna152 is fixed relative to the aperture of the antenna 152. For example,the antenna 152 may be a direct radiating two-dimensional array whichresults in boresight being normal to a plane containing the antennaelements of the array. As another example, the antenna 152 may be areflector antenna. In such a case, the antenna 152 can be fullymechanically steered by the positioner 220 to point the beam at thetarget satellite 110. For example, the positioner 220 may be anelevation-over-azimuth (EL/AZ), two-axis positioner that providesadjustment in azimuth and elevation. As another example, the positioner220 may be a three-axis positioner to provide adjustment in azimuth,elevation and skew.

In some embodiments, the antenna 152 is an electro-mechanically steeredarray that includes one mechanical scan axis and one electrical scanaxis, such as a variably inclined continuous transverse stub (VICTS)antenna. In such a case, the pointing adjustment mechanism can include acombination of mechanical and electrical scanning mechanisms.

In some embodiments, the antenna 152 is a non-movable, fully electronicscanned phased array antenna. In such a case, the pointing adjustmentmechanism can include feed networks and phase controlling devices toproperly phase signals communicated with some or all of the antennaelements of the antenna 152 to scan the beam in azimuth and elevation.

As mentioned above, the antenna control unit 270 provides a controlsignal on line 272 to positioner 220 to point the beam of the antenna152. The functions of the antenna control unit 270 can be implemented inhardware, instructions embodied in memory and formatted to be executedby one or more general or application specific processors, firmware, orany combination thereof.

During normal operation, as the aircraft 102 moves relative to thetarget satellite 110, the antenna control unit 270 provides the controlsignal on line 272 to positioner 220 to point the beam of the antenna152 in the appropriate angular position in the direction of the targetsatellite 110. The antenna control unit 270 may determine theappropriate angular position based on the location of the targetsatellite 110, the location of the aircraft 102, and the attitude(including yaw, roll, and pitch) of the aircraft 102. The antennacontrol unit 270 may for example store (or otherwise obtain) dataindicating the location of the target satellite 110. The geographiclocation of the aircraft 102 may for example be obtained via a globalpositioning system (GPS) 274 or other equipment on the aircraft 102. Theattitude of the aircraft 102 may for example be provided via an inertialreference unit (IRU) 380 on the aircraft 102.

From time to time, the antenna control unit 270 also provides thecontrol signal on line 272 to perform a re-pointing process describedherein to reduce pointing error at the target satellite 110, while alsoavoiding excessive interference with the non-target satellite 120. Asdescribed in more detail below, the re-pointing process described hereintakes into consideration the interference requirement of the non-targetsatellite 120 when determining whether or not to perform a particular(e.g., preferred or default) mispointing correction operation. Thisparticular mispointing correction operation is referred to hereinafteras a “first mispointing correction operation”.

When the antenna system 150 (and thus the aircraft 102) is at certaingeographic locations, the intentional mispointing introduced by thefirst mispointing correction operation is such that the antenna system150 still satisfies interference requirement with the non-targetsatellite 120. In other words, the interference due to the combinationof an expected pointing error (e.g., a maximum or peak pointing error)at the target satellite 110 and the intentional mispointing, is withinacceptable limits (i.e., below a threshold) to the non-target satellite120. These certain geographic locations are referred to herein as an“acceptable geographic region” for performing the first mispointingcorrection operation. The geographic locations that are within theacceptable geographic region, and whether it is continuous ordiscontinuous, can vary from embodiment to embodiment depending onvarious factors described below. Outside of the acceptable geographicregion, the use of the particular mispointing correction operation isprecluded due to the interference requirement. It is worth noting thatthe antenna system 150 may still be used for normal operations outsidesome or all of the acceptable geographic region, as the interference dueto the worst-case pointing error without intentional mispointing may byitself still be within acceptable limits to the non-target satellite120.

The value of the threshold below which the amount of amount ofinterference to the non-target satellite 120 is acceptable can forexample be based on regulatory requirements imposed by regulatoryagencies (e.g., FCC, ITU, etc.) on the maximum power spectral density(or other metric) that can be radiated to the non-target satellite 120,and/or coordination agreements with the operator of the non-targetsatellite 120. Additionally, the threshold can account for pointingaccuracy limitations of the antenna 152 during normal operations.

The antenna control unit 270 can determine whether or not to perform thefirst mispointing correction operation based on whether or not thecurrent geographic location of the aircraft 102 is within the acceptablegeographic region. The current geographic location may for example beprovided via the GPS 274 or other equipment on the aircraft 102.

The amount of interference if the first mispointing correction operationwere performed at a given geographic location can be determined usingvarious techniques, and can be characterized or represented in differentways. For example, in some embodiments the amount of interference isrepresented in terms of power spectral density (PSD).

The amount of uplink interference can for example be determined basedone or more of the known antenna pattern characteristics of the antenna152, the transmission parameters (e.g., transmit power, frequency range,etc.) of the return uplink signal 116, the parameters (e.g., angularpositions) of the first mispointing correction operation, the geographiclocation of the aircraft 102, the attitude of the aircraft 102, thelocations of the target satellite 110 and non-target satellite 120, theoperating frequency, system gain-to-noise temperature (G/T) and/orpolarization of operation of the non-target satellite 120, etc.Alternatively, other and/or additional information can be used tocalculate the amount of interference. The amount of downlinkinterference can be calculated in a similar manner based on theparameters of a signal from the non-target satellite 120 that isreceived by the antenna system 150.

In some embodiments, the comparison of the threshold amount ofinterference to the amount of interference at the various geographiclocations if the first mispointing correction operation were performedhas been previously calculated. In such a case, the antenna control unit270 (or other component) can store a look-up table indicating whether ornot performing the first mispointing correction operation is permittedat each the various geographic locations.

In embodiments in which one or both of the target satellite 110 and thenon-target satellite 120 are non-geostationary satellites, theacceptable geographic region may change over time depending on thecurrent locations of the target satellite 110 and the non-targetsatellite 120. For example, at a first time, the effective angularseparation between the target satellite 110 and the non-target satellite120 as viewed at a particular geographic location may be small enoughthat the interference due to intentional mispointing of the firstmispointing correction operation would exceed the threshold. However, ata second time, due to the movement of the target satellite 110 relativeto the non-target satellite 120, the effective angular separation asviewed at that particular geographic location may be large enough thatthe first mispointing correction operation can be performed while stillsatisfying the interference requirement. In such a case, the look-uptable may include the various possible locations of the target satellite110 and/or the non-target satellite 120. The antenna control unit 270may determine whether or not performing the first mispointing correctionoperation is permitted based on the current locations of the targetsatellite 110 and/or the non-target satellite 120.

During the first mispointing correction operation, the antenna controlunit 270 can provide control signal on line 272 to positioner 220 toadjust the beam of the antenna 152 to various angular positions of acorrection profile (discussed below). At the same time, the antennacontrol unit 270 obtains an indication of signal strength (or othersignal metric such as signal-to-noise ratio, bit-error rate, etc.) of asignal communicated with the target satellite 110 while at the variousangular positions. The manner in which the beam of the antenna 152 isadjusted to the various angular positions is discussed in more detailbelow.

In the illustrated embodiment, the antenna control unit 270 obtains areceived signal strength indicator (RSSI) from the transceiver 210 (orthe modem 230 or other component) indicating the signal strength of theforward downlink signal 114 received by the antenna 152 at the variousangular positions. Alternatively, other techniques may be used. Forexample, in some embodiments, the mispointing correction operation mayalso or alternatively use the signal strength (or other signal metric)of a signal transmitted by the antenna 152 to the target satellite 110,such as the return uplink signal 116. In such a case, the antennacontrol unit 270 may obtain the value of signal strength (or othersignal metric) of the return uplink signal 116 that was received by thetarget satellite 110 from the gateway terminal 130 (or other elements ofthe satellite communications system 100 such as a core node, NOC, etc.)via the forward downlink signal 114.

The antenna control unit 270 can then select the final angular positionto point the beam of the antenna 152 based on the measured signal metricat the various angular positions. The antenna control unit 270 may use avariety of techniques to select the final angular position. For example,the antenna control unit 270 may fit the measurements to a 2-D or 3-Dcurve depending upon the correction profile of the first mispointingcorrection operation, and then select the angular position correspondingto the maximum signal metric (e.g., maximum signal strength).Alternatively, other techniques may be used. The antenna control unit270 can then provide the control signal to the positioner 220 to adjustthe beam of the antenna 152 to point in the selected angular position.The antenna control unit 270 can then return to normal operations, andprovide further adjustments to the angular position of the beam as theaircraft 102 moves relative to the target satellite 110.

FIG. 3 illustrates a perspective view of an example of antenna 152 andpositioner 220 of antenna system 150. In the illustrated embodiment, theantenna 152 includes an array 310 of antenna elements that is a directradiating two-dimensional array which results in boresight being normalto a plane containing the antenna elements of the array 310.Alternatively, the array 310 of antenna elements can be arranged or fedin a different manner such that boresight is not normal to the planecontaining the antenna elements of the array 310. As mentioned above, inother embodiments the antenna type of the antenna 152 may be different.

The positioner 220 is responsive to control signal provided by theantenna control unit 270 (see FIG. 2) to point the beam of the antenna152 at the target satellite 110. In the illustrated embodiment, thepositioner 220 is an elevation-over-azimuth (EL/AZ) two-axis positionerthat provides full two-axis mechanical steering. The positioner 220includes a mechanical azimuth adjustment mechanism to move the beam ofthe antenna 152 is azimuth 320, and a mechanical elevation adjustmentmechanism to move the beam of the antenna 152 is elevation 340. Each ofthe mechanical adjustment mechanisms can for example include a motorwith gears and other elements to provide for movement of the antenna 152around a corresponding axis. As mentioned above, in other embodimentsthe pointing adjustment mechanism used to point the beam of the antenna152 may be different than positioner 220.

FIG. 4 illustrates an example process 400 for operating the antennasystem 150 including performing an example re-pointing process 404 bythe antenna control unit 270 of FIG. 2. Other embodiments can combinesome of the steps, can perform the steps in different orders and/orperform different or additional steps to the ones illustrated in FIG. 3.

During step 402, the antenna system 150 is in normal operation, and asignal is communicated between the antenna system 150 on the aircraft102 and the target satellite 110. In embodiments in which the antennasystem 150 is in bidirectional communication with the target satellite110, multiple signals (e.g., forward downlink signal 114, and returnuplink signal 116) may be communicated during this step. As describedabove, as the aircraft 102 moves relative to the target satellite 110,the antenna control unit 270 provides the control signal on line 272 topositioner 220 to point the beam of the antenna 152 in the appropriateangular position in the direction of the target satellite 110.

Next, the re-pointing process 404 is initiated. The manner in which there-pointing process 404 is initiated can vary from embodiment toembodiment. In examples described below, the antenna control unit 270determines when to begin the re-pointing process 304, without receivinga command from an external device. In alternative embodiments, anexternal device may determine when to begin the re-pointing process 304and provide a command to the antenna control unit 270. The command mayfor example be transmitted to the antenna control unit 270 by thegateway terminal 130 (or other elements of the satellite communicationssystem 100 such as a core node, NOC, etc.) via the forward downlinksignal 114. As another example, the command may be received from otherequipment (e.g., modem 230, transceiver 210, etc.) of the antenna system150 or other equipment on the aircraft 102.

The factor (or factors) by which the determination is made by theantenna control unit 270 to begin the re-pointing process 404 can varyfrom embodiment to embodiment. For example, in some embodiments there-pointing process 404 is initiated upon determining that the antennasystem 150 (and thus aircraft 102) has entered the acceptable geographicregion for performing the first mispointing correction operation.Further examples of the factor (or factors) that may be used arediscussed in more detail below with respect to FIGS. 9-12.

After starting the re-pointing process 404 at step 406, at step 408 theantenna control unit 270 obtains the current geographic location of theaircraft 102. The current geographic location of the aircraft 102 mayfor example be obtained from the GPS 274.

At step 410, the antenna control unit 270 determines whether the currentgeographic location is within the acceptable geographic region forperforming the first mispointing correction operation. As describedabove, antenna control unit 270 may store a look-up table indicatingwhether or not performing the first mispointing correction operation ispermitted at various geographic locations. In such a case, the antennacontrol unit 270 may use the look-up table to determine whether or notthe first mispointing correction operation is permitted at the currentgeographic location.

If the determination is made that the current geographic location iswithin the acceptable geographic region, the process 400 continues tostep 412. At step 412, the first mispointing correction operation isperformed as discussed above. The re-pointing process 404 then ends atstep 416.

If the determination is made that the current geographic location is notwithin the acceptable geographic region, the first mispointingcorrection operation is precluded due to the interference requirementwith the non-target satellite 120, and the process 400 skips step 412and ends at step 316. After step 416, the process 300 returns to step302 and normal operation of the antenna system 150 resumes.

FIG. 5 illustrates an example of a correction profile 505 of the firstmispointing correction operation versus azimuth and elevation angles. Inthe illustrated embodiment, the correction profile 505 is a two axisoperation that simultaneously moves in both azimuth and elevation.Alternatively, the correction profile 505 may be different.

The plot of FIG. 5 is a projection of the angular positions onto a planethat is perpendicular to the initial angular position 500 extending outof the page. The correction profile 505 indicates the changes in azimuthand elevation angles relative to the initial angular position 500. Atthe beginning of the first mispointing correction operation, the initialangular position 500 is the direction the positioner 220 is pointing thebeam of the antenna 152. As mentioned above, pointing error may havebeen introduced since the last mispointing correction operation wasperformed due to various factors. As a result, the initial angularposition 500 may not correspond to the actual direction of the targetsatellite 110. In some embodiments, during the mispointing correctionoperation the antenna control unit 270 may continue to make adjustmentsto the initial angular position of the beam due to movement of theaircraft 102 relative to target satellite 110 in order to track thetarget satellite 110. In such a case, the actual values of the azimuthand elevation angles of the initial angular position 500 of thecorrection profile 505 may change during the mispointing correctionoperation. As a result, since the correction profile 505 is relative tothe initial angular position 500, the actual values of the azimuth andelevation angles may also change.

As can be seen in FIG. 5, the correction profile 505 in FIG. 5 moves theangular position of the beam of the antenna 512 in a circular manner vs.time (counter-clockwise in this example). In other words, the correctionprofile 505 relative to the initial angular position 500 has a radiusand an angular velocity. Alternatively, the correction profile 505 maybe non-circular, such as being elliptical.

The antenna control unit 270 controls the positioner 220 to adjust theangular position of the beam of the antenna 152 along the correctionprofile 505. As mentioned above, at the same time, the antenna controlunit 270 obtains an indication of signal strength (or other signalmetric) of a signal (e.g., forward downlink signal 114) communicatedwith the target satellite 110 at various angular positions along thecorrection profile 505.

In the illustrated embodiment, the angular positions at whichmeasurements are made include a first pair of angular positions 510, 530along the azimuth axis, and a second pair of angular positions 520, 540along the elevation axis. In other embodiments, the number of angularpositions may be different such as including one or more intermediateangular positions between angular positions 510, 520, 530, 540, and/ormay be oriented relative to azimuth axis and elevation axis in adifferent manner.

The number of cycles the beam is moved around the correction profile 505can vary from embodiment to embodiment. Upon completing the desirednumber of cycles of the correction profile 505, the antenna control unit270 can then estimate the actual direction of the target satellite 110based on the final signal metric measurements made at the variousangular positions. In some embodiments, the antenna control unit 270 mayalso obtain the signal metric when the beam of the antenna 152 waspointed at the initial angular position 500. A least-squares regressionanalysis or other technique may then be performed by the antenna controlunit 270 to form a 3-D curve fitting the measured data. The antennacontrol unit 270 can then select the final angular positioncorresponding to the maximum signal metric of the 3-D curve.

The antenna control unit 270 can then provide the control signal to thepositioner 220 to adjust the beam of the antenna 152 to point in theselected angular position. The antenna control unit 270 can then returnto normal operations, and provide further adjustments to the angularposition of the beam as the aircraft 102 moves around relative to thetarget satellite 110.

FIG. 6 illustrates an example of an acceptable geographic region 650,652 for performing the first mispointing correction operation. In theillustrated embodiment, the target satellite 110 and the non-targetsatellite 120 are each geostationary satellites.

In the illustrated embodiment, the target satellite 110 is a multi-spotbeam satellite that includes spot beams 600, 610 having correspondingcoverage areas. The corresponding coverage area may be any suitableshape.

Each spot beam provides communication service to terminals located atgeographic locations within its corresponding coverage area. For eachspot beam (e.g. spot beam 600), the satellite G/T is typically highestnear the center of its coverage area and decreases towards the edges.Although only two spot beams 600, 610 are shown to avoid overcomplication of the drawing, the target satellite 110 may include manymore spot beams.

In the illustrated embodiment, the antenna system 150 on the aircraft102 employs return-link power control by making adjustments to thetransmit power of transceiver 210, so that a particular power level ofthe return uplink signal 116 is maintained at the target satellite 110.A variety of open- or closed-loop power control techniques may be used.

Because the satellite G/T roll off towards the edges of each spot beam,in order to maintain the particular power level at the satellite 102 theantenna system 150 makes corresponding adjustments to the transmit powerof the transceiver 210 as the aircraft 102 moves along a path 612. Forexample, the transmit power of the transceiver 210 when the aircraft 102is at location 614 within spot beam 600 is higher than the transmitpower when the aircraft 102 is at location 616 closer to the center ofthe spot beam 600.

Increasing the transmit power level toward the edges of each spot beamalso increases the amount of interference generated by the antennasystem 150 with the non-target satellite 120. In particular, thesehigher transmit power levels near the edges can result in excessiveinterference with the non-target satellite 120, if the first pointingcorrection operation were also performed there. As a result, in theillustrated embodiment, the acceptable geographic region 650 and 652 forperforming the first mispointing correction operation are due to thereturn-link power control and corresponds to centers of the coverageareas of the spot beams 600, 610 of the target satellite 110.

The acceptable geographic region 650, 652 are geographic locations ofthe antenna system 150 (and thus the aircraft 102) where the amount ofinterference with the non-target satellite 120 when performing the firstmispointing correction operation is below the threshold. In other words,within the acceptable geographic region 650, 652, the transmit power issufficiently low enough that the intentional mispointing introducedduring the first mispointing correction operation does not causeexcessive interference with the non-target satellite 120.

FIG. 7 illustrates an example process 700 for operating the antennasystem 150 including performing an example re-pointing process 704 bythe antenna control unit 270 of FIG. 2. As compared to the re-pointingprocess 404 of FIG. 4, the re-pointing process 704 of FIG. 7 includesstep 714. The other steps of the re-pointing process 704 of FIG. 7 canbe the same as the steps described above with respect to FIG. 4, andthus a description of those steps is not repeated here.

As shown in FIG. 7, if the determination is made at step 410 that thecurrent geographic location is not within the acceptable geographicregion for performing the mispointing correction operation, the process400 continues to step 714. At step 714, a second mispointing correctionoperation is performed. The re-pointing process 404 then ends at step416.

The second mispointing correction operation of step 714 has one or moreparameters that are different than the first mispointing correction ofstep 712, such that that second mispointing correction operation can beperformed outside of the acceptable geographic region for performing themispointing correction operation. Thus, at a particular geographiclocation that is outside the acceptable geographic region for performingthe mispointing correction operation, the second mispointing correctionoperation is such that the antenna system 150 still satisfiesinterference requirement with the non-target satellite 120.

In the illustrated embodiment, the second mispointing correctionoperation can be performed at all locations outside the acceptablegeographic region of the first mispointing correction operation. Thus,the process 700 automatically performs step 714 if step 412 cannot beperformed. In other embodiments, the second mispointing operation ofstep 714 may not be automatically performed. In such a case, after step410, the antenna control unit 270 may determine whether the currentgeographic location is within the acceptable geographic region forperforming the second mispointing correction operation. The techniquesfor determining whether the second mispointing correction operation canbe performed at the current geographic location, can be similar totechniques described above for step 410.

The manner in which the second mispointing correction operation differsfrom the first mispointing correction operation can vary from embodimentto embodiment.

In some embodiments, one or more transmission parameters of the returnuplink signal 116 during the second mispointing correction operation aredifferent than that of the return uplink signal 116 during the firstmispointing correction operation. For example, the antenna system 150can change one or more of the transmitted power level of the returnuplink signal 116, spreading the return uplink signal 116 over a largerbandwidth, or any other technique for reducing the power spectraldensity in the direction of the non-target satellite 120. Thus, ifeither one can be used while satisfying the interference requirementwith the non-target satellite 120, the first mispointing correctionoperation may be preferred because it permits more efficientcommunication with the target satellite 110 than the second mispointingcorrection operation. In one embodiment, transmission of the returnuplink signal 116 is muted (i.e., turned off) during the secondmispointing correction operation.

In some embodiments, one or more angular positions along a correctionprofile of the second mispointing correction operation is different thanthe correction profile of the first mispointing correction operation.Examples of the differences between the corrections profiles of thefirst and second mispointing correction operations are discussed in moredetail below with respect to FIG. 8.

In some embodiments in which the beam of the antenna 152 has anasymmetric beam pattern, the determination of whether to perform thefirst correction operation takes into account the skew angle of thebeam. The asymmetric beam pattern can be due to a non-circular antennaaperture of the antenna 152. The non-circular shape can be due to thecombination of electrical performance requirements and size constraints.Specifically, the non-circular antenna aperture can be designed to havea large enough effective area to provide sufficient antenna gain tosatisfy link requirements between the aircraft 102 and the targetsatellite 110, while also having a swept volume small enough that it canbe housed under an aerodynamic radome. The asymmetric beam pattern has anarrow beamwidth axis along the longest dimension of the non-circularantenna aperture, and a wide beamwidth axis along the shortest dimensionof the non-circular antenna aperture. For example, in the rectangularaperture of the example shown in FIG. 3, the narrow beamwidth axis isalong a major axis (the longest line through the center of the array310) of the aperture, and the wide beamwidth axis is along a minor axis(the shortest line through the center of the array 310) of the aperture.

As used herein, “skew angle” refers to the angle between the narrowbeamwidth axis of the beam of the antenna 152, and a line defined by thetarget satellite 110 and the non-target satellite 120. The half-powerbeamwidth of the beam of the antenna 152 along the line defined by thetarget satellite 110 and the non-target satellite 120 is referred toherein as a “composite half-power beamwidth”. The composite half-powerbeamwidth is a mixture of the half-power beamwidths along the narrowbeamwidth axis and the wide beamwidth axis respectively, and depends onthe skew angle. For example, in embodiments in which the targetsatellite 110 and the non-target satellite 120 are geostationarysatellites along the geostationary arc, the skew angle is the anglebetween the narrow beamwidth axis and the geostationary arc, and thecomposite half-power beamwidth is the beamwidth along the geostationaryarc.

The skew angle, and thus the composite half-power beamwidth, variesdepending upon the geographic location of the aircraft 102. For example,if the antenna system 150 is located at the same longitude as the targetsatellite 110, the skew angle is zero degrees and the compositehalf-power beamwidth is the half-power beamwidth along the narrowbeamwidth axis. In such a case, the composite half-power beamwidth maybe narrow enough that intentional mispointing introduced during thefirst mispointing correction operation still permits the antenna system150 to satisfy the interference requirement with the non-targetsatellite 120. However, if the antenna system 150 is located at adifferent longitude than the target satellite 110, the skew angle isnon-zero and the composite half-power beamwidth is a mixture of thehalf-power beamwidths along the narrow beamwidth axis and the widebeamdwidth axis. As a result, at certain geographic locations, thecomposite half-power beamdwidth can be wide enough to cause excessiveinterference with the non-target satellite 120, if the first mispointingcorrection operation were used. In such a case, the acceptablegeographic region for performing the first mispointing correctionoperation can correspond to geographic locations wherein the skew anglethat is at or below a skew angle threshold, where a skew angle above thethreshold would result in excessive interference with the non-targetsatellite 120 if the first mispointing correction operation wereperformed. At skew angles above the skew angle threshold, performing thefirst mispointing correction operation is precluded. Thus, in theexample of FIG. 7, if it is determined in step 410 that the firstmispointing operation is precluded due to the skew angle, the secondmispointing correction operation of step 714 may be performed. In theexample of FIG. 4, if it is determined in step 410 that the firstmispointing operation is precluded due to the skew angle, step 412 isskipped.

FIG. 8 illustrates an example of a correction profile 805 of the secondmispointing correction operation as described herein. In the illustratedembodiment, the correction profile 805 is a two axis operation thatsimultaneously moves in both azimuth and elevation. Also shown in FIG. 8is the example correction profile 505 of the first mispointingcorrection operation described in FIG. 5.

Similar to the discussion above with respect to the correction profile505 of the first mispointing correction operation, during the secondmispointing correction operation the antenna control unit 270 controlsthe positioner 220 to adjust the angular position of the beam of theantenna 152 along the correction profile 805. At the same time, theantenna control unit 270 obtains an indication of signal strength (orother signal metric) of a signal (e.g., forward downlink signal 114)communicated with the target satellite 110 at the various angularpositions along the correction profile 805.

In the illustrated embodiment, the angular positions at whichmeasurements are made include a first pair of angular positions 860, 880along the azimuth axis, and a second pair of angular positions 870, 890along the elevation axis. In other embodiments, the number of angularpositions may be different such as including one or more intermediateangular positions between angular positions 860, 870, 880, 890, and/ormay be oriented relative to azimuth axis and elevation axis in adifferent manner.

The number of cycles the beam is moved around the correction profile 805can vary from embodiment to embodiment. Upon completing the desirednumber of cycles of the correction profile 805, the antenna control unit270 can then estimate the actual direction of the target satellite 110based on the final signal metric measurements made at the variousangular positions along the correction profile 805. In some embodiments,the antenna control unit 270 may also obtain the signal metric when thebeam of the antenna 152 was pointed at the initial angular position 500.A least-squares regression analysis or other technique may then beperformed by the antenna control unit 270 to form a 3-D curve fittingthe measured data. The antenna control unit 270 can then select thefinal angular position corresponding to the maximum signal metric of the3-D curve.

The antenna control unit 270 can then provide the control signal to thepositioner 220 to adjust the beam of the antenna 152 to point in theselected angular position. The antenna control unit 270 can then returnto normal operations, and provide further adjustments to the angularposition of the beam as the aircraft 102 moves around relative to thetarget satellite 110.

In the illustrated embodiment, the range of angular positions of thecorrection profile 805 is reduced by the same amount in both the azimuthaxis and the elevation axis compared to that of the correction profile505. In other words, the amount of reduction of the angular values ofthe correction profile 805 is independent of the particular azimuth andelevation angles. In other embodiments, the range of angular positionsof the correction profile 805 is not reduced by the same amount in boththe azimuth axis and the elevation axis compared to that of thecorrection profile 505.

In some embodiments the reduction in the range of angular positions ofthe correction profile 805 compared to the correction profile 505 takesinto account the angular position of the non-target satellite 110. Asthe aircraft 102 moves around to various geographic locations, theangular position of the non-target satellite 120, as viewed in theazimuth/elevation coordinate system of the antenna system 150, willchange. For example, in embodiments in which the target satellite 110and the non-target satellite 120 are geosynchronous satellites, athigher latitudes around the same longitude of the target satellite 110,the non-target satellite 120 is mostly or entirely along the azimuthaxis of the antenna system 150. However, at lower latitudes near theequator and at different longitudes of the target satellite 110, thenon-target satellite 120 is mostly or entirely along the elevation axisof the antenna system 150.

Thus, in some embodiments the angular positions of the correctionprofile 805 compared to the correction profile 505 may be selectivelyreduced in the direction of the non-target satellite 120 sufficient tosatisfy the interference requirement. In such a case, at angularpositions where moving along the correction profile 505 does not exceedthe interference requirement, the angular values of those angularpositions of the correction profile 805 may be the same as that of thecorrection profile 505.

In embodiments in which the antenna 152 has an asymmetric beam, thereduction in the angular positions of the correction profile 805compared to the correction profile 505 may take into account the skewangle. As mentioned above, the skew angle and thus the compositehalf-power beamwidth of the beam of the antenna 152 along the linebetween the target satellite 110 and the non-target satellite 120,varies depending on the geographic location of the aircraft 102. Thus,in some embodiments the angular positions of the correction profile 805compared the correction profile 505 may be reduced in the direction ofthe non-target satellite 120 by an amount that is based on the skewangle sufficient to satisfy the interference requirement. For example,if the antenna system 150 is at a first geographic location such thatthe skew angle is a first value above the skew angle threshold, theangular values of some or all of the angular positions in the directionof the non-target satellite 110 may be reduced by a first amount inorder to satisfy the interference requirement. If the antenna system 150is at a second geographic location such that the skew angle is a secondvalue greater than the first value, the composite half-power beamwidthof the beam of the antenna 152 is greater than when at the firstgeographic location. Accordingly, when the aircraft 102 is at the secondgeographic location, the angular values of some or all of the angularpositions may be reduced by a second amount that is greater than thefirst amount in order to satisfy the interference requirement. In someembodiments, the amount of reduction for a given skew angle isindependent of the particular azimuth and elevation angles. In otherembodiments, the reduction is only in the direction of the non-targetsatellite 110.

The appropriate angular positions of the correction profile 805 for thevarious geographic locations of the aircraft 102 can be pre-computed andstored in the look-up table by the antenna control unit 270. The antennacontrol unit 270 can then use the current geographic location of theaircraft 102 to retrieve the appropriate angular positions of thecorrection profile 805 from the look-up table. Alternatively, othertechniques may be used to obtain the appropriate angular positions.

As a result of the reduced angular range, the amount of intentionalmispointing during the second mispointing correction operation is lessthan that of the first mispointing correction operation. This in turnresults in a lower amount of interference with the non-target satellite120 than the first mispointing correction operation.

At some or all of the geographic locations within the acceptablegeographic region of the first mispointing correction operation, thefirst mispointing correction operation may provide more accuratepointing (i.e., less residual pointing error) at the target satellitethan the second mispointing correction operation. For example, movingfurther away from the initial angular direction 500 may provide a moreaccurate estimate of the actual direction of the target satellite 110when subsequently curve-fitting to the measured signal metrics. This isbecause the difference between measured signal metrics increases withincreasing movement away from initial angular direction 500. This inturn makes the estimate of the actual direction of the target satellite110 less susceptible to non-positional signal fluctuations or noise, andthus results in a more accurate estimate of the actual direction. Insome embodiments, at some or all of the angular positions of thecorrection profile 805 having reduced angle values compared to that ofthe correction profile 505, the duration of the measurement may beincreased in order to lessen the pointing error impact due to not movingas far away from the initial angular direction.

Thus, the first mispointing correction operation may be preferred overthe second mispointing correction operation, if either one can be usedwhile satisfying the interference requirement with the non-targetsatellite 120. However, by performing the second mispointing correctionoperation, the pointing error can be reduced in geographic locationswhere use of the first mispointing correction operation is precluded.This in turn can improve the pointing accuracy and thus resourceefficiency of satellite communication system 100, as compared to notperforming any mispointing correction operation at those locations.

FIG. 9 illustrates an example process 900 for operating the antennasystem 150 including performing the example re-pointing process 704 ofFIG. 7. Other embodiments can combine some of the steps, can perform thesteps in different orders and/or perform different or additional stepsto the ones illustrated in FIG. 9. As compared to the process 700 ofFIG. 7, the process 900 of FIG. 9 includes step 902. The other steps ofFIG. 9 can be the same as the steps described above with respect to FIG.7, and thus a description of those steps is not repeated here.

As shown in FIG. 9, the re-pointing process 704 is initiated if thenominal correction interval is exceeded. The nominal correction intervalis a predetermined time interval (e.g., 15 minutes) between which there-pointing process 404 should be performed. If at step 902 it isdetermined that the amount of time since previously performing there-pointing process 404 exceeds the predetermined time interval, there-pointing process 704 is initiated.

The predetermined time interval can vary from embodiment to embodiment.The predetermined time interval may for example correspond to the amountof time it is expected to take for the pointing error to increase to acertain pointing error limit. The predetermined time interval may forexample be determined empirically (e.g., by comparing correction offsetsand estimating the typical rate the offset difference increases withtime), or calculated (e.g., by using a heading drift value from adatasheet of the IRU 280).

FIG. 10 illustrates an example process 1000 for operating the antennasystem 150 including performing the example re-pointing process 704 ofFIG. 7. Other embodiments can combine some of the steps, can perform thesteps in different orders and/or perform different or additional stepsto the ones illustrated in FIG. 10. As compared to the process 700 ofFIG. 7, the process 1000 of FIG. 10 includes step 1002. The other stepsof FIG. 10 can be the same as the steps described above with respect toFIG. 7, and thus a description of those steps is not repeated here.

As shown in FIG. 10, the repointing process 704 is initiated if thepredicted pointing error exceeds a pointing error limit. If at step 1002it is determined that predicted pointing error exceeds the pointingerror limit, the re-pointing process 704 is initiated. The predictedpointing error may be calculated using various techniques that can takeinto consideration one or more of the factors that can cause thepointing error to increase with time, such as drift of a navigationsensor (e.g., an inertial reference unit (IRU) 280) on the aircraft 102,structural deflections of the aircraft 102 caused by takeoff, movementand other disturbances, etc.

In some embodiments, the predicted pointing error takes intoconsideration the drift characteristics of the IRU 280. The antennacontrol unit 270 may for example integrate the worst-case drift rate ofthe IRU 280 over time to determine its pointing error contribution. Theworst-case drift rate may for example be determined empirically and theresults stored in the look-up table. In some embodiments, the IRU 280may operate in a GPS augmentation mode when the aircraft 102 is inmotion and valid geographic location data is available from the GPS 274,and operate in a free inertial mode when either of these conditions arenot met. In such a case, the worst-case drift rate used by the antennacontrol unit 270 may depend on the current operational mode the IRU 280.

In some embodiments, the predicted pointing error takes intoconsideration the flight characteristics of the aircraft 102. Forexample, the estimated pointing error may include a fuselage flexurepointing error if it is determined by the antenna control unit 270 (orother component) that the aircraft 102 has taken off since the lastre-pointing process. The fuselage flexure pointing error may bedetermined empirically and stored in the look-up table. The fuselageflexure pointing error may depend on various factors including theaircraft type, etc. The manner in which it is determined that takeoff ofthe aircraft 102 has occurred can vary from embodiment to embodiment.For example, the antenna control unit 270 may determine that takeoff hasoccurred based on changes in the groundspeed and altitude data providedby the IRU 280. Alternatively, other techniques may be used.

FIG. 11 illustrates an example process 1100 for operating the antennasystem 150 including performing example re-pointing process 704 of FIG.7. Other embodiments can combine some of the steps, can perform thesteps in different orders and/or perform different or additional stepsto the ones illustrated in FIG. 11.

As shown in FIG. 11, the repointing process 704 is initiated if theaircraft 102 is approaching an edge of the acceptable geographic regionfor performing the first mispointing correction operation. If at step1102 it is determined that the aircraft 102 is within a predetermineddistance from an edge, the re-pointing process 704 is initiated. Theparticular geographic locations that are the predetermined distance froman edge may for example be predetermined and be stored in the look-uptable. The antenna control unit 270 can then use the look-up table todetermine whether to initiate the repointing process 704 based on thecurrent location of the aircraft 102.

In the example of FIG. 11, the repointing process 704 is initiated atstep 1102, and then at step 410 it is determined whether the aircraft102 is within the acceptable geographic region for performing the firstmispointing correction operation. Alternatively, at step 1102 it may bedetermined whether the aircraft 102 is within the acceptable geographicregion for performing the first mispointing correction operation. Insuch a case, the step 410 and subsequent step 714 may be omitted fromthe process 1100.

FIG. 12 illustrates an example process 1200 for operating the antennasystem 150 including performing the example re-pointing process 704 ofFIG. 7. Other embodiments can combine some of the steps, can perform thesteps in different orders and/or perform different or additional stepsto the ones illustrated in FIG. 12.

Step 402 can be the same as described above with respect to FIGS. 4 and7, and thus a description of that step is not repeated here.

At step 1202, the antenna control unit 270 determines whether thenominal correction interval is exceeded. Step 1202 may be the same asstep 902 discussed above with respect to FIG. 9. If the nominalcorrection interval is exceeded, the process 1200 initiates there-pointing process 704 and then returns to step 402. If the nominalcorrection interval is not exceeded, the process 1200 moves to step1204.

At step 1204, the antenna control unit 270 determines whether thepointing error limit is exceeded. Step 1204 may be the same as step 1002of FIG. 10. If the pointing error limit is exceeded, the process 1200initiates the re-pointing process 704 and then returns to step 402. Ifthe pointing error limit is not exceeded, the process 1200 moves to step1206.

At step 1206, the antenna control unit 270 determines whether theaircraft 102 is approaching an edge of the acceptable geographic regionfor performing the first mispointing correction operation. Step 1206 maybe the same as step 1102 of FIG. 11. If the aircraft 102 is approachingan edge of the acceptable geographic region, the process 1200 initiatesthe re-pointing process 704 and then returns to step 402. If theaircraft 102 is not approaching an edge of the acceptable geographicregion, the process returns to step 402.

The methods disclosed herein include one or more actions for achievingthe described method. The methods and/or actions can be interchangedwith one another without departing from the scope of the claims. Inother words, unless a specific order of actions is specified, the orderand/or use of specific actions can be modified without departing fromthe scope of the claims.

The functions described can be implemented in hardware, software,firmware, or any combination thereof. If implemented in software, thefunctions can be stored as one or more instructions on a tangiblecomputer-readable medium. A storage medium can be any available tangiblemedium that can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can include RAM, ROM, EEPROM,CD-ROM, or other optical disk storage, magnetic disk storage, or othermagnetic storage devices, or any other tangible medium that can be usedto carry or store desired program code in the form of instructions ordata structures and that can be accessed by a computer. Disk and disc,as used herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers.

A computer program product can perform certain operations presentedherein. For example, such a computer program product can be a computerreadable tangible medium having instructions tangibly stored (and/orencoded) thereon, the instructions being executable by one or moreprocessors to perform the operations described herein. The computerprogram product can include packaging material. Software or instructionscan also be transmitted over a transmission medium. For example,software can be transmitted from a website, server, or other remotesource using a transmission medium such as a coaxial cable, fiber opticcable, twisted pair, digital subscriber line (DSL), or wirelesstechnology such as infrared, radio, or microwave.

Further, modules and/or other appropriate means for performing themethods and techniques described herein can be downloaded and/orotherwise obtained by suitable terminals and/or coupled to servers, orthe like, to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a CD or floppy disk, etc.), such that a user terminal and/orbase station can obtain the various methods upon coupling or providingthe storage means to the device. Moreover, any other suitable techniquefor providing the methods and techniques described herein to a devicecan be utilized. Features implementing functions can also be physicallylocated at various positions, including being distributed such thatportions of functions are implemented at different physical locations.

While the present disclosure is disclosed by reference to the preferredembodiments and examples detailed above, it is to be understood thatthese examples are intended in an illustrative rather than in a limitingsense. It is contemplated that modifications and combinations willreadily occur to those skilled in the art, which modifications andcombinations will be within the spirit of the invention and the scope ofthe following claims.

What is claimed is:
 1. A method comprising: communicating a signalbetween an antenna system on a mobile vehicle and a target satellite;determining that an expected amount of interference by the communicatedsignal with a non-target satellite due to intentional mispointing of theantenna system for a first mispointing correction operation is below athreshold; and performing the first mispointing correction operationbased at least in part on the determination that the expected amount ofinterference is below the threshold, wherein performing the firstmispointing correction operation comprises: adjusting a beam of theantenna system from an initial angular position toward the targetsatellite to a plurality of angular positions and obtaining a signalmetric of the communicated signal at the plurality of angular positions,and positioning the beam of the antenna system relative to the initialangular position based on the obtained signal metric of the communicatedsignal at the plurality of angular positions.
 2. The method of claim 1,wherein determining that the expected amount of interference by thecommunicated signal with the non-target satellite is below the thresholdcomprises determining one or more of: an antenna pattern characteristicof the antenna system, a transmit power of a return uplink signal, afrequency range of the return uplink signal, a range of angularpositions of the first mispointing correction operation, a location ofthe mobile vehicle, an attitude of the mobile vehicle, a location of thetarget satellite, a location of the non-target satellite, an operatingfrequency, a system gain-to-noise temperature (G/T), and a polarizationof an operation of the non-target satellite.
 3. The method of claim 1,wherein determining that the expected amount of interference by thecommunicated signal with the non-target satellite is below the thresholdcomprises: determining a location of the mobile vehicle; and determininga value of a look-up table based at least in part on the location of themobile vehicle, wherein the look-up table indicates whether or notperforming the first mispointing correction operation is permitted at aplurality of locations including the location of the mobile vehicle. 4.The method of claim 1, further comprising: after performing the firstmispointing correction operation, determining that a second expectedamount of interference by a second communicated signal with thenon-target satellite due to intentional mispointing of the antennasystem for a second mispointing correction operation meets or exceedsthe threshold; and performing the second mispointing correctionoperation based at least in part on the determination that the secondexpected amount of interference meets or exceeds the threshold, whereinthe second mispointing correction operation has one or more parametersdifferent than the first mispointing correction operation to maintaininterference with the non-target satellite below the threshold.
 5. Themethod of claim 4, wherein the one or more parameters includes one ormore of a transmit power of the communicated signal, a range of angularpositions about at least one axis of the antenna system, and a durationof measurement of the communicated signal at an angular position.
 6. Themethod of claim 1, further comprising determining if an amount of timesince previously performing the first mispointing correction operationexceeds a predetermined time interval, and wherein the performing thefirst mispointing correction operation of the antenna system is furtherbased at least in part on a determination that the amount of timeexceeds the predetermined time interval.
 7. The method of claim 1,further comprising determining if a predicted pointing error of the beamof the antenna system towards the target satellite exceeds a pointingerror limit, and wherein the performing the first mispointing correctionoperation of the antenna system is further based at least in part on adetermination that the predicted pointing error exceeds the pointingerror limit.
 8. The method of claim 1, further comprising determining ifthe mobile vehicle is within a predetermined distance from an edge of anacceptable geographic region in which the expected amount ofinterference with the non-target satellite by the communicated signalduring the first mispointing correction operation is below thethreshold, and wherein the performing the first mispointing correctionoperation of the antenna system is further based at least in part on adetermination that the mobile vehicle is within the predetermineddistance.
 9. The method of claim 8, wherein: the communicated signal isan uplink signal transmitted from the antenna system to the targetsatellite; and performing the first mispointing correction operationuses a downlink signal received by the antenna system from the targetsatellite.
 10. The method of claim 9, wherein: the target satellitecomprises a plurality of spot beams; the antenna system adjusts a powerlevel of the uplink signal based on a position of the mobile vehiclewithin coverage areas of the plurality of spot beams; and the acceptablegeographic region for performing the first mispointing correctionoperation corresponds to centers of the coverage areas of the pluralityof spot beams.
 11. The method of claim 1, further comprising: afterperforming the first mispointing correction operation, determining thata second expected amount of interference by a second communicated signalwith the non-target satellite due to intentional mispointing of theantenna system for the first mispointing correction operation meets orexceeds the threshold, wherein the second communicated signal is anuplink signal transmitted from the antenna system to the targetsatellite; muting transmission of the uplink signal; and performing thefirst mispointing correction operation.
 12. The method of claim 1,wherein the mobile vehicle is one of an aircraft, a boat or a train. 13.An antenna system for mounting on a mobile vehicle, the antenna systemcomprising: an antenna having a beam for communicating a signal with atarget satellite; a pointing adjustment mechanism coupled to the antennaand responsive to control signals to adjust an angular position of thebeam of the antenna; and an antenna control unit to: determine that anexpected amount of interference by the communicated signal with anon-target satellite due to intentional mispointing of the antennasystem for a first mispointing correction operation is below athreshold; and provide a control signal to the pointing adjustmentmechanism to perform the first mispointing correction operation based atleast in part on the determination that the expected amount ofinterference is below the threshold, wherein performing the firstmispointing correction operation comprises: adjusting the beam of theantenna system from an initial angular position toward the targetsatellite to a plurality of angular positions and obtaining a signalmetric of the communicated signal at the plurality of angular positions,and positioning the beam of the antenna system relative to the initialangular position based on the obtained signal metric of the communicatedsignal at the plurality of angular positions.
 14. The antenna system ofclaim 13, wherein the antenna control unit is configured to determinethat the expected amount of interference by the communicated signal withthe non-target satellite is below the threshold by determining one ormore of: an antenna pattern characteristic of the antenna system, atransmit power of a return uplink signal, a frequency range of thereturn uplink signal, a range of angular positions of the firstmispointing correction operation, a location of the mobile vehicle, anattitude of the mobile vehicle, a location of the target satellite, alocation of the non-target satellite, an operating frequency, a systemgain-to-noise temperature (G/T), and a polarization of an operation ofthe non-target satellite.
 15. The antenna system of claim 13, whereinthe antenna control unit is configured to determine that the expectedamount of interference by the communicated signal with the non-targetsatellite is below the threshold by: determining a location of themobile vehicle; and determining a value of a look-up table based atleast in part on the location of the mobile vehicle, wherein the look-uptable indicates whether or not performing the first mispointingcorrection operation is permitted at a plurality of locations includingthe location of the mobile vehicle.
 16. The antenna system of claim 13,wherein the antenna control unit is further to: after the pointingadjustment mechanism performs the first mispointing correctionoperation, determine that a second expected amount of interference by asecond communicated signal with the non-target satellite due tointentional mispointing of the antenna system for a second mispointingcorrection operation meets or exceeds the threshold; and provide asecond control signal to the pointing adjustment mechanism to performthe second mispointing correction operation based at least in part onthe determination that the second expected amount of interference meetsor exceeds the threshold, wherein the second mispointing correctionoperation has one or more parameters different than the firstmispointing correction operation to maintain interference with thenon-target satellite below the threshold.
 17. The antenna system ofclaim 16, wherein the one or more parameters includes one or more of atransmit power of the communicated signal, a range of angular positionsabout at least one axis of the antenna system, and a duration ofmeasurement of the communicated signal at an angular position.
 18. Theantenna system of claim 13, wherein the antenna control unit is furtherto determine if an amount of time since previously performing the firstmispointing correction operation exceeds a predetermined time interval,and wherein the antenna control unit is further to provide the controlsignal to the pointing adjustment mechanism to perform the firstmispointing correction operation of the antenna system based at least inpart on a determination that the amount of time exceeds thepredetermined time interval.
 19. The antenna system of claim 13, whereinthe antenna control unit is further to determine if a predicted pointingerror of the beam of the antenna system towards the target satelliteexceeds a pointing error limit, and wherein the antenna control unit isfurther to provide the control signal to the pointing adjustmentmechanism to perform the first mispointing correction operation of theantenna system based at least in part on a determination that thepredicted pointing error exceeds the pointing error limit.
 20. Theantenna system of claim 13, wherein the antenna control unit is furtherto determine if the mobile vehicle is within a predetermined distancefrom an edge of an acceptable geographic region in which the expectedamount of interference with the non-target satellite by the communicatedsignal during the first mispointing correction operation is below thethreshold, and wherein the antenna control unit is further to providethe control signal to the pointing adjustment mechanism to perform thefirst mispointing correction operation of the antenna system the antennasystem based at least in part on a determination that the mobile vehicleis within the predetermined distance.
 21. The antenna system of claim20, wherein: the communicated signal is an uplink signal transmittedfrom the antenna system to the target satellite; and the pointingadjustment mechanism performs the first mispointing correction operationusing a downlink signal received by the antenna system from the targetsatellite.
 22. The antenna system of claim 21, wherein: the targetsatellite comprises a plurality of spot beams; the antenna systemadjusts a power level of the uplink signal based on a position of themobile vehicle within coverage areas of the plurality of spot beams; andthe acceptable geographic region for performing the first mispointingcorrection operation corresponds to centers of the coverage areas of theplurality of spot beams.
 23. The antenna system of claim 13, wherein theantenna control unit is further to: after the pointing adjustmentmechanism performs the first mispointing correction operation, determinethat a second expected amount of interference by a second communicatedsignal with the non-target satellite due to intentional mispointing ofthe antenna system for the first mispointing correction operation meetsor exceeds the threshold, wherein the second communicated signal is anuplink signal transmitted from the antenna system to the targetsatellite; mute transmission of the uplink signal; and provide a secondcontrol signal to the pointing adjustment mechanism to perform the firstmispointing correction operation.
 24. The antenna system of claim 13,wherein the mobile vehicle is one of an aircraft, a boat or a train.